how are you starting the command prompt?
why didn't i think of this earlier
in the same folder as the FILE.mdl you want to convert and uncombine.class create a new .txt file
in this text file put:
where FILE is the name of the file you want to uncombine
actually, you could use FILE.png or .jpg or .gif or any of the other formats supported by java's imageIO
rename your text file so its extension is .bat
run the batch file